\text{The equation} (1+k)\cdot\frac{\cos x\cdot\cos(2x-\alpha)}{\cos(x-\alpha )} =1+k\cos 2x \; has no repeated root in it's domain of definition, if :
a) |k| ≤ |csc α| , k ≠± 1
a) |k| ≤ |csc α| , k ≠- 1
a) |k| ≥ |csc α| , k ≠± 1
a) |k| ≥ |csc α| , k ≠- 1
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